1. Field of the Invention
The present invention relates to a printed circuit board unit including a printed wiring board and an electronic component package mounted on the printed wiring board. The electronic component package includes a heat spreading member covering over a predetermined surface of an electronic component such as a LSI (Large-Scale Integrated circuit) chip. The heat spreading member extends larger than the predetermined surface of the electronic component.
2. Description of the Prior Art
A LSI package includes a LSI chip mounted on a small-sized printed wiring board. A heat spreading member or heat spreader is received on the upper surface of the LSI chip. A solidified material, such as a solidified silver paste, a solidified diamond paste, or the like, having heat conductivity is interposed between the LSI chip and the heat spreader. The solidified material serves to improve an efficient transfer of heat from the LSI chip to the heat spreader. The heat is allowed to spread over a larger or wider area of the heat spreader.
The small-sized printed wiring board may utilize a substrate made of resin in the LSI package, for example. Such a substrate, however, tends to suffer from a larger expansion as compared with the LSI chip in response to a rise in temperature of the LSI chip, for example, because of the linear expansivity larger than that of the LSI chip. This results in a slight camber of the substrate. The camber of the substrate causes separation between the heat spreader and the solidified material. An efficient transfer of heat cannot thus be accomplished between the LSI chip and the heat spreader.